(a(i))[1]
a pair of wires.
(a(ii))[1]
a coaxial cable link.
(a(iii))[1]
microwave radiation.
(b)[2]
State two advantages that optic fibres have compared with coaxial cables for long-range communication.
(c(i))[2]
An optic fibre has length $62\,\text{km}$ and an attenuation per unit length of $0.21\,\text{dB km}^{-1}$. The input power to the fibre is $P$. At the receiver, the noise power is $9.2\,\mu\text{W}$. The signal-to-noise ratio at the receiver is $25\,\text{dB}$. Calculate the ratio, in dB, of the input power $P$ to the noise power at the receiver.
(c(ii))[2]
Use your answer in (i) to find the input power $P$.